1. Field of the Invention
The present invention relates to a stream data reproducing system.
2. Description of the Related Art
A stream processing method is a method for reading data flowing without interruption (hereinafter referred to as stream data) to be processed next, while starting processing of the stream data including a header portion concurrently with the detection of the header portion of the stream data, instead of executing predetermined processing after reading all the data in a memory of a personal computer or the like.
Examples of such stream data, in the MPEG method known as a data compression/extension technology, include a data string of video data encoded in compliance with an MPEG video part (video stream data), a data string of audio data encoded in compliance with an MPEG audio part (audio stream data), a data string (system stream data) obtained by time-division multiplexing and merging the MPEG video stream data and MPEG audio stream data in compliance with an MPEG system part and the like. Supply sources of the streams (hereinafter referred to as a “stream source”) cover a broad spectrum including optical discs such as CD-ROM, DVD and the like, memory devices such as a flash memory for a portable audio device and the like, antennas for Broadcasting Satellite (to be known as BS), digital terrestrial broadcast, or car navigation systems or the like.
FIG. 10 is a diagram illustrating the configuration of a stream data reproducing system. In the following, for the sake of convenience of explanation, an MPEG audio stream data reproducing system stored in an optical disc will be described as an example of a stream data reproducing system (See Japanese Patent Laid-Open No. 2003-216195, for example).
A stream source 10 is an optical disc in which audio stream data compressed by an MPEG inter-frame prediction is stored. A single frame (referred to as AAU (Audio Access Unit)) constituted by a plurality of words, which is a decodable minimum processing unit of such audio stream data includes a header, an error correcting code, and audio data, from the beginning to the end.
An input buffer 20 is a buffer constituted by an FIFO ring buffer, for example, for sequentially accumulating audio stream data read out by an optical pickup from the stream source 10 and A/D converted.
An output buffer 30 is a buffer constituted by an FIFO ring buffer, for example, similarly to the input buffer 20, for sequentially accumulating decode data generated as a decode result of the audio stream data by a DSP 50.
An output device 40 is constituted by an amplifier-mounted speaker, for example, and outputs voice of decode data sequentially supplied from the output buffer 30 and D/A converted.
The DSP (digital Signal Processor) 50 is generally characterized by: being provided with a DSP core 52 including a product-sum multiplier which is able to execute product-sum operation at a high speed or the like; employment of a Harvard architecture in which a data memory 51 and a program memory 53 are separated and accessed independently from the DSP core 52; etc. The DSP 50 executes the following decode processing for the audio stream data accumulated in the input buffer 20.
That is, the DSP core 52 detects a header portion of each single frame of the audio stream data accumulated in the input buffer 20, and outputs a read request to the input buffer 20 based on the detection result. As a result, the audio stream data is read out by the unit of a single word from the input buffer 20 to input to the DSP 50. The DSP core 52 outputs a write request to the data memory 51, to write the audio stream data read out from the input buffer 20 into a predetermined region (stream buffer) of the data memory 51.
The DSP core 52 reads out an MPEG decode processing program stored in the program memory 53, to execute predetermined decode processing (extension processing or the like) to the audio stream data stored in the data memory 51. The decode data generated by the result of decode processing is written in a predetermined region (decode buffer) of the data memory 51 by the DSP 52. And the DSP core 52 outputs a read request to the data memory 51, reads out the decode data stored in the data memory 51 by the unit of a single word, and supplies it to the output buffer 30. As a result, voice output is made from the output device 40, and decode processing by the DSP 50 is completed.
In an example illustrated in FIG. 10, the DSP core 52 reads out the audio stream data from the input buffer 20, to be extended into the data memory 51. The DSP core 52 also reads out the decode data written in the data memory 51, to be written into the output buffer 30.
Such a stream data reproducing system employs a system that data transfer is repeatedly carried out by the unit of one word between the input/output buffer and the DSP. Thus, a processing load according to the data transfer with the input/output buffer makes up a large proportion of the entire processing load of the DSP, which hinders innate decode processing of the DSP.